Field of the Invention
The present invention relates to a slewing control device for a hybrid construction machine, and a hybrid construction machine provided with the slewing control device.
Description of the Related Art
In recent years, slewing construction machines such as shovels and cranes are configured such that, in order to reliably stop and hold a slewing superstructure, a mechanical brake as well as position holding control for holding the slewing superstructure in a current position is used to stop and hold the slewing superstructure.
Japanese Patent No. 3977697 discloses the following technology. Specifically, as illustrated in FIG. 4 of Japanese Patent No. 3977697, when an operation lever is operated to the center side with respect to positions LnL and LnR, position holding control for holding a slewing superstructure in a current position is started based on a signal from a position sensor. Then, in Japanese Patent No. 3977697, when the operation lever is operated to the center side with respect to positions LbL and LbR (positions closer to the center than the positions LnL and LnR), the operation of a mechanical brake is started. Then, in Japanese Patent No. 3977697, when the operation lever is operated to the center side with respect to positions LzL and LzR (positions closer to the center than the positions LbL and LbR), the position holding control is finished.
In Japanese Patent No. 3977697, although the position holding control is finished at the positions LzL and LzR, the position holding control is finished without having determined whether or not a braking force of the mechanical brake is sufficiently effective. Therefore, in Japanese Patent No. 3977697, if the braking force of the mechanical brake is insufficient when the operation lever reaches the position LzL or LzR, the slewing superstructure may move in a slewing direction due to the action of the gravitational force, that is, so-called “slewing-down movement” may occur. In particular, when the construction machine is located on an inclined ground, the gravitational force applied to the slewing superstructure in the direction to slew the slewing superstructure is increased to increase the possibility of the occurrence of slewing-down movement.